This invention relates to variable capacity vane compressors which are adapted for use as refrigerant compressors of air conditioners for automotive vehicles.
A variable capacity vane compressor is known e.g. by Japanese Provisional Utility Model Publication No. 55-2000 filed by the same assignee of the present application, which is capable of controlling the capacity of the compressor by varying the suction quantity of a gas to be compressed. According to this known vane compressor, arcuate slots are formed in a peripheral wall of the cylinder and each extend from a lateral side of a refrigerant inlet port formed through the same peripheral wall of the cylinder and also through an end plate of the cylinder, and in which is slidably fitted a throttle plate, wherein the effective circumferential length of the opening of the refrigerant inlet port is varied by displacing the throttle plate relative to the slot so that the compression commencing position in a compression chamber defined in the cylinder and accordingly the compression stroke period varies to thereby vary the capacity or delivery quantity of the compressor. A link member is coupled at one end to the throttle plate via a support shaft secured to the end plate, and at the other end to an actuator so that the link member is pivotally displaced by the actuator to displace the throttle plate.
However, according to the conventional vane compressor, because of the intervention of the link member between driving means or the actuator and a control member or the throttle plate for causing displacement of the throttle plate, the throttle plate undergoes a large hysteresis, leading to low reliability in controlling the compressor capacity, and also the capacity control mechanism using the link member, etc. requires complicated machining and assemblage.
Further, a variable capacity vane compressor which has a reduced hysteresis of the control member is known by Japanese Provisional Patent Publication (Kokai) No. 61-232397 filed by the same assignee of the present application, which provides an improvement in a vane compressor comprising a cylinder formed of a cam ring and a pair of side blocks closing opposite ends of the cam ring, a rotor rotatably received within the cylinder, a plurality of vanes radially slidably fitted in respective slits formed in the rotor, a control member disposed for displacement in a refrigerant inlet port formed in one of the side blocks, and driving means for causing the control member to be displaced relative to the refrigerant inlet port, whereby the capacity or delivery quantity of the compressor can be varied by displacement of the control member. The improvement comprises driven teeth provided on the control member, and driving teeth provided on an output shaft of the driving means in mating engagement with the driven teeth, whereby the control member is driven directly by the driving means through the mating driving and driven teeth.
However, according to this conventional vane compressor, a stepping motor as the driving means is mounted within the compressor housing, requiring a large space for accommodation of the stepping motor, and the capacity control mechanism has an overall complicated construction and accordingly is high in manufacturing cost.
The first-mentioned conventional vane compressor is disposed to vary the circumferential length of the opening of the refrigerant inlet port by displacing the throttle plate relative to the slot, that is, to vary a circumferential angle at which the refrigerant inlet port is closed with respect to the position of the vane, which is hereinafter referred to as "closing angle".
FIG. 1 shows the operating regions which the vane passes to execute one operating cycle of a conventional vane compressor in which the refrigerant inlet port is closed at a fixed angle, and FIG. 2 shows load on the vane with respect to rotational angle of the rotor of the compressor.
In FIG. 1, symble a designates the rotor, b a vane slit radially formed in the rotor a, c a vane slidably fitted in a vane slit b, d a vane back-pressure chamber defined in the rotor a at an inner end of a slit b in the rotor a, e a communication groove formed at an end face of the rotor a such that it arcuately extends through a predetermined angle and is communicated with each vane back-pressure chamber d, f a cam ring, g a refrigerant inlet port formed in a side block h, and i a refrigerant outlet port formed in the cam ring f, respectively. In such vane compressor wherein the regrigerant inlet port is closed at a fixed angle, the fixed angle .theta. at which the refrigerant inlet port is closed is, for example, set at approximately 45 degrees in the forward rotational direction of the rotor a from a circumferential location at which a clearance between an outer peripheral surface of the rotor a and the inner peripheral surface of the cam ring f assumes the minimum value. The region extending through approximately 45 degrees corresponds to the suction stroke, i.e. a suction pressure Ps area where the suction pressure is introduced into a compression chamber j. A region extends through 75 degrees in the forward rotational direction of the rotor a from the terminating end of the suction pressure area Pa, which corresponds to the compression stroke, where the pressure within the compression chamber j increases from the suction pressure Ps to a discharge pressure Pd. A region extends through 60 degrees in the forward rotational direction of the rotor a from the terminating end of the compression stroke, which corresponds to the discharge stroke, i.e. a discharge pressure Pd area where the compressed refrigerant is discharged. The circumferential position and circumferential length of the arcuate communication groove e are set such that the outer end of the vane c is always kept in contact with the inner peripheral surface of the cam ring f. Back pressure Pk within each vane back-pressure chamber d is determined by the difference between an amount of refrigerant gas flowing from a high pressure zone or a discharge pressure chamber, not shown, into the vane back-pressure chamber d by way of the communication groove e and one flowing from the vane back-pressure chamber d into a suction chamber, not shown. In FIG. 1, it is clear that the pressure increasing area between the suction pressure Ps area and the discharge pressure area Pd, and the discharge pressure Pd area are larger in total circumferential angle than the suction pressure Ps area as a low pressure area, so that the amount of refrigerant gas flowing from the discharge chamber into the vane back-pressure chamber d is always greater than one flowing from the back-pressure chamber d into the suction chamber. Therefore, the vane back pressure Pk acting on the inner end face of the vane c (the force urging the vane c toward the outer periphery of the rotor a) is always greater than the high pressure acting on the outer end face of the vane c (the force urging the vane c toward the center of the rotor a), which results in that the outer end of the vane c is always kept in contact with the inner peripheral surface of the cam ring f.
On the other hand, in the above-described conventional variable capacity vane compressor, in which the angle at which the refrigerant inlet port is closed or the closing angle is variable, the closing angle is so small during full capacity that the pressure increasing area between the suction pressure Ps area and the discharge pressure Pd area, and the discharge pressure Pd area are larger in total circumferential angle than the suction pressure Ps area, as similarly to the vane compressor of fixed closing angle type as shown in FIG. 1. Thus, there is no problem during the full capacity operation. However, there occurs the following problem during partial capacity operation. During the partial capacity operation, the closing angle .theta. of the inlet port g is closed is approximately 100 degrees in the forward rotational direction of the rotor a from the circumferential location at which the clearance between the outer peripheral surface of the rotor a and the inner peripheral surface of the cam ring f is the minimum, as shown in FIG. 3. The region extending through approximately 100 degrees corresponds to the suction stroke, i.e. a suction pressure Ps area where the suction pressure is introduced into a compression chamber j. A region extends through 40 degrees in the forward rotational direction of the rotor a from the terminating end of the suction pressure Ps area, which corresponds to the compression stroke, where the pressure within the compression chamber j increases from the suction pressure Ps to a discharge pressure Pd. A region extends through 40 degrees in the forward rotational direction of the rotor a from the terminating end of the compression stroke, which corresponds to the discharge stroke, i.e. a discharge pressure Pd area where the compressed refrigerant is discharged. The pressure increasing area between the suction pressure Ps area and the discharge pressure area Pd, and the discharge pressure Pd area are smaller in total circumferential angle than the suction pressure Ps area as a low pressure area, so that the amount of refrigerant gas flowing from the back-pressure chamber d into the suction chamber becomes greater than one flowing from the discharge chamber into the vane back-pressure chamber d. Therefore, the vane back pressure Pk acting the inner end face of the vane c becomes smaller than that during the full capacity operation, as shown in FIG. 4. Especially, in the vicinity of the terminating end of the compression stroke, as indicated by simble A in FIG. 4, the vane back pressure Pk acting on the inner end face of the vane c becomes smaller than the high pressure acting on the outer end face of the vane c, which results in that the outer end of the vane c becomes separated from the inner peripheral surface of the cam ring f. In the worst case, the compression is not performed. Further, when the outer end of the vane c becomes separated from the inner peripheral surface of the cam ring f, the vane back pressure Pk acting on the inner end face of the vane c surpasses the discharge pressure Pd acting on the outer end face, wherery the outer end of the vane c is again brought into contact with the inner peripheral surface of the cam ring f. In this way, the outer end of the vane c are alternately brought into or out of contact with the inner peripheral surface of the cam ring f during every one rotation of the rotor a, causing chattering noise.